1. Field of the invention:
This invention relates to an apparatus for dispersing spacers on the substrate of a liquid-crystal display panel that define the space between the upper and lower substrates of the display panel.
2. Description of the prior art:
The basic structure of liquid-crystal display panels has, as shown in FIG. 4, two substrates 31 and 32 spaced at a fixed distance from each other, which form a space into which liquid crystals 33 are sealed. The size of this space is usually referred to as the "cell thickness".
To obtain a liquid-crystal display panel that has satisfactory display qualities, it is necessary that the cell thickness be uniform within the display field. To make uniform the cell thickness of the liquid-crystal display panel, a method is widely used in which fine spacers 35 are dispersed so as to be incorporated into the space between the two substrates 31 and 32. As these spacers, glass fibers, spherical beads made of plastic, spherical beads of an inorganic material, and the like can be used. The conventional methods for dispersing these spacers over the substrate includes:
(1) a spraying method in which the spacers are suspended in a volatile solvent, and the resulting suspension is sprayed over the substrate; and
(2) a dipping method in which the spacers are suspended in a solvent, and the substrate is immersed in the suspension and pulled out of the suspension.
Of these methods, the first method, in which a volatile solvent is used, often involves the use of freon solvents, petroleum solvents, or the like. It is difficult for these solvents to evaporate completely when dispersed together with spacers over liquid-crystal display panels. Thus, the residual components and impurities in the organic solvent may give rise to a poor display, which introduces a problem in the quality of the finished product.
Also, in the second method, spacers are dispersed in an organic solvent, a liquid-crystal aligning agent such as polyimide, or the like, and the substrate is immersed in the mixture, then being pulled slowly out of the mixture so that the spacers will adhere to the substrate. However, when this method is used, there are problems in that the spacers are not uniformly dispersed on the surface of the solvent, that the adhesion of the spacers is affected by fluctuations in the surface tension caused by changes in the state of the substrate surface, and the like. Thus, it is difficult to disperse the spacers uniformly over the entire surface of the substrate.